1. Field of the Invention
The present invention relates to a power roller unit for a toroidal-type continuously variable transmission.
2. Description of the Related Art
It has been enforced in part of the car industry to use such a toroidal-type continuously variable transmission as shown in FIGS. 3 and 4 as a transmission for a car. In this toroidal-type continuously variable transmission, an input side disk 2 is supported concentrically with an input shaft 1 and an output side disk 4 is fixed to the end portion of an output shaft 3 which is disposed concentrically with the input shaft 1. In the interior of a casing in which the toroidal-type continuously variable transmission is stored, there are disposed trunnions 6, 6 which can be swung about their respective pivot shafts 5, 5 disposed at positions twisted with respect to the input shaft 1 and output shaft 3.
That is, each of the trunnions 6, 6, as shown in FIG. 5 and FIG. 7 which will be discussed later, includes a pair of bent wall portions 8, 8 respectively formed in the longitudinal-direction (in FIGS. 5 and 7, in the right and left direction) two end portions of a support plate portion 7 constituting the trunnion 6 in such a manner that they are curved to the inner surface side (in FIG. 5, left side) of the support plate portion 7. And, due to the two bent wall portions 8, 8, in the trunnion 6, there is formed a recess-shaped pocket portion P for storing a power roller 11 (which will be discussed later) therein. Also, on the outer surfaces of the respective bent wall portions 8, 8 (on the opposite surfaces thereof to the support plate portion 7), there are disposed their associated pivot shafts 5, 5 in such a manner that they are concentric with each other.
In the middle portion of the support plate portion 7, there is formed a circular hole 10, while the base end portion of a displacement shaft 9 is supported in the circular hole 10. And, in case where the trunnions 6, 6 are swung about their respective pivot shafts 5, 5, the inclination angles of the displacement shafts 9, 9 supported on the middle portions of the trunnions 6, 6 can be adjusted. Also, on the peripheries of the leading end portions of displacement shafts 9, 9 projected from the inner surfaces of their respective support plate portions 7, 7, there are rotatably supported power rollers 11, 11; and, the power rollers 11, 11 are interposed between and held by the input side and output side disks 2, 4. By the way, the base end portions and leading end portions of the respective displacement shafts 9, 9 are formed eccentric to each other.
The sections of the mutually opposing inner surfaces 2a, 4a of the input side and output side disks 2, 4 are respectively formed as concave surfaces which can be obtained by rotating an arc the center of which is the pivot shaft 5 or by rotating a curved line near to such arc. And, the peripheral surfaces 11a, 11a (which are respectively formed as spherical-shaped convex surfaces) of the respective power rollers 11, 11 are contacted with the respective inner surfaces 2a, 4a. 
Between the input shaft 1 and input side disk 2, there is interposed a pressing device 12 of a loading cam type. This pressing device 12 presses the input side disk 2 toward output side disk 4 elastically. Also, the pressing device 12 is composed of a cam plate 13 rotatable together with the input shaft 1 and a plurality of (for example, four) rollers 15, 15 respectively held by a retainer 14. Also, in one side surface (in FIGS. 3 and 4, the left side surface) of the cam plate 13, there is formed a cam surface 16, that is, an uneven surface which extends in the peripheral direction of such one side surface; and, also in the outer surface (in FIGS. 3 and 4, the right side surface) of the input side disk 2, there is formed a similar cam surface 17. And, the plurality of rollers 15, 15 are supported in such a manner that they can be rotated about axes which extend in the radial direction with respect to the input shaft 1.
In the thus-structured toroidal-type continuously variable transmission, in case where the input shaft 1 is rotated, with the rotation of the input shaft 1, the cam plate 13 is rotated and thus the cam surface 16 presses the plurality rollers 15, 15 against the cam surface 17 formed in the outer surface of the input side disk 2. As a result of this, not only the input side disk 2 is pressed against the plurality of power rollers 11, 11 but also, due to the mutual pressing between the pair of cam surfaces 16, 17 and the plurality of rollers 15, 15, the input side disk 2 is rotated. And, the rotation power of the input side disk 2 is transmitted through the power rollers 11, 11 to the output side disk 4, thereby being able to rotate the output shaft 3 fixed to the output side disk 4.
To change the rotation speed between the input shaft 1 and output shaft 3, specifically, to reduce the rotation speed between the input shaft 1 and output shaft 3, the trunnions 6, 6 may be respectively swung about their associated pivot shafts 5, 5 and the displacement shafts 9, 9 may be thereby inclined so that the peripheral surfaces 11a, 11a of the power rollers 11, 11, as shown in FIG. 3, can be contacted with the near-to-center portion of the inner surface 2a of the input side disk 2 and the near-to-outer-periphery portion of the inner surface 4a of the output side disk 4.
On the other hand, to increase the rotation speed between the input shaft 1 and output shaft 3, the trunnions 6, 6 may be respectively swung and the displacement shafts 9, 9 may be thereby inclined so that the peripheral surfaces 11a, 11a of the power rollers 11, 11, as shown in FIG. 4, can be contacted with the near-to-outer-periphery portion of the inner surface 2a of the input side disk 2 and the near-to-center portion of the inner surface 4a of the output side disk 4. In case where the inclination angles of the displacement shafts 9, 9 are set in the intermediate angles between the inclination angles shown in FIGS. 3 and 4, there can be obtained an intermediate transmission ratio between the input shaft 1 and output shaft 3.
Further, FIGS. 6 and 7 show a conventionally known toroidal-type continuously variable transmission. In this toroidal-type continuously variable transmission, an input side disk 2 and an output side disk 4 are respectively supported on the periphery of a circular-pipe-shaped input shaft 18 in such a manner that they can be rotated as well as can be shifted in the axial direction through their associated needle roller bearings 19, 19. Also, a cam plate 13, which constitutes a pressing device 12 of a loading cam type, is spline engaged with the outer peripheral surface of the end portion (in FIG. 6, the left end portion) of the input shaft 18; and, a flange portion 20 prevents the cam plate 13 from moving in the direction to part away from the input side disk 2. Also, an output gear 21 is connected to the output side disk 4 by keys 22, 22, while the output side disk 4 and output gear 21 can be rotated in synchronization with each other.
On the two end portions of each of a pair of trunnions 6, 6 having such a structure as shown in the previously discussed FIG. 5, there are disposed pivot shafts 5, 5; and, these pivot shafts 5, 5 are supported in such a manner that they can be swung with respect to a pair of support plates 23, 23 and can be shifted in the axial direction (in FIG. 6, in the front and back direction; and, in FIG. 7, in the right and left direction) with respect to the support plates 23, 23. That is, the pivot shafts 5, 5 are respectively supported inside support holes 23a formed in the support plates 23, 23 by their associated radial needle roller bearings 32. And, in circular holes 10 which are respectively formed in the middle portions of the support plate portions 7, 7 of the trunnions 6, 6, there are rotatably supported the base end portions 9a of displacement shafts 9 structured such that their base end portions 9a and leading end portions 9b are arranged in parallel to each other and are eccentric to each other. Also, on the peripheries of the leading end portions 9b, 9b of the respective displacement shafts 9, 9 that are projected from the inner surfaces of their associated support plate portions 7, 7, there are rotatably supported power rollers 11, 11.
By the way, a pair of displacement shafts 9, 9, which are disposed on each pair of trunnions 6, 6, are situated at positions on the 180-degree opposite side to each other with respect to the input shaft 18. Also, the direction, in which the leading end portions 9b of the displacement shafts 9, 9 are eccentric to their associated base end portions 9a, is the same direction (in FIG. 7, in the reversed right and left direction) with respect to the rotation direction of the input side and output side disks 2, 4. And, the eccentric direction is substantially perpendicular to the mounting direction of the input shaft 18. Therefore, the power rollers 11, 11 are supported in such a manner that they can be shifted slightly in the longitudinal direction of the input shaft 18. As a result of this, even in case where the power rollers 11, 11 tend to shift in the axial direction of the input shaft 18 due to the elastic deformation of the respective composing parts of the toroidal-type continuously variable transmission caused by thrust loads generated by the pressing device 12, such shifting motion of the power rollers 11 can be absorbed with no unreasonable forces being applied to the composing parts.
Also, between the outer surfaces of the respective power rollers 11, 11 and the inner surfaces of the support plate portions of the respective trunnions 6, 6, there are interposed thrust ball bearings 24 and thrust needle roller bearings 25, both of which belong to thrust rolling bearings, sequentially in the order starting at and from the outer surface side of the power roller 11. Of these bearings, the thrust ball bearings 24, while supporting thrust-direction loads applied to the respective power rollers 11, allow these power rollers 11 to rotate. Each of the thrust ball bearings 24 is composed of a plurality of balls 26, 26, a circular-ring-shaped retainer 27 for holding these balls 26, 26 in a rollable manner, and a circular-ring-shaped outer ring 28. Also, the inner raceways of the respective thrust ball bearings 24 are formed in the outer surfaces of the respective power rollers 11, while the outer raceways thereof are formed in the inner surfaces of the respective outer rings 28.
Also, the thrust needle roller bearings 25 are respectively held by and between the inner surfaces of the support plate portions 7, 7 and the outer surfaces of the outer rings 28. These thrust needle roller bearings 25, while supporting thrust loads applied to the outer rings 28 from the power rollers 11, 11, allow the power rollers 11, 11 and outer rings 28 to be swung and shifted about the centers of the base end portions 9a of the displacement shafts 9.
Further, to the one-end portions (in FIG. 7, the left end portions) of the respective trunnions 6, 6, there are connected drive rods 29; and, to the outer peripheral surfaces of the middle portions of the respective drive rods 29, there are fixed drive pistons 30 respectively. And, the drive pistons 30 are respectively oil-tight fitted into their associated drive cylinders 31.
In the case of the thus-structured toroidal-type continuously variable transmission, the rotation power of the input shaft 18 is transmitted through the pressing device 12 to the input side disk 2. And, the rotation power of the input side disk 2 is transmitted through the pair of power rollers 11, 11 to the output side disk 4 and further the rotation power of the output side disk 4 is taken out from the output gear 21.
To change the rotation speed ratio between the input shaft 18 and output gear 21, the pair of drive pistons 30, 30 may be shifted in the mutually opposite directions. As the drive pistons 30, 30 are shifted, the pair of trunnions 6, 6 are shifted in the mutually opposite directions. For example, the power roller 11 shown on the lower side in FIG. 7 is shifted to the right in FIG. 7, whereas the power roller 11 on the upper side in FIG. 7 is shifted to the left in FIG. 7. This changes the directions of tangential-direction forces that are applied to the contact portions between the peripheral surfaces 11a, 11a of the power rollers 11, 11 and the inner surfaces 2a, 4a of the input side disk 2 and output side disk 4. With such change in the directions of the tangential-direction forces, the trunnions 6, 6 are caused to swing in the mutually opposite directions about their associated pivot shafts 5, 5 which are pivotally supported on the support plates 23, 23.
As a result of this, as shown in the previously discussed FIGS. 3 and 4, the contact positions between the peripheral surfaces 11a, 11a of the power rollers 11, 11 and the inner surfaces 2a, 4a are changed, thereby changing the rotation speed ratio between the input shaft 18 and output gear 21. Also, in case where the torque to be transmitted between the input shaft 18 and output gear 21 is varied and the elastic deformation amounts of the respective composing parts of the toroidal-type continuously variable transmission are thereby varied, the respective power rollers 11, 11 and the outer rings 28 belonging to these power rollers 11 are slightly rotated about the base end portions 9a of their associated displacement shafts 9. Such rotational movements of the power rollers 11 and outer rings 28 are made smoothly, because the thrust needle roller bearings 25 are respectively interposed between the outer surfaces of the outer rings 28 and the inner surfaces of the support plate portions 7, 7 of the trunnions 6, 6. Therefore, as has been described before, there is required only a small force to change the inclination angles of the respective displacement shafts 9, 9.
When the above-structured toroidal-type continuously variable transmission is in operation, thrust loads are applied to the power rollers 11, which are rotatably supported on the inner surface sides (pocket portion P sides) of the respective trunnions 6, 6, from the inner surfaces 2a, 4a of the input side and output side disks 2, 4. And, these thrust loads are transmitted through the thrust ball bearings 24 and thrust needle roller bearings 25 to the inner surfaces of the respective trunnions 6, 6. Therefore, when the toroidal-type continuously variable transmission is in operation, the respective trunnions 6, 6, as shown exaggeratedly in FIG. 5, are elastically deformed only slightly in the direction where the inner surface sides of the trunnions 6 with the power rollers 11 disposed thereon provide concave surfaces.
And, in case where the elastic deforming amounts of the trunnions 6 increase, the thrust loads, which are applied to the balls 26, 26 serving as rolling bodies constituting the thrust ball bearings 24 and needle rollers constituting the thrust needle roller bearings 25, become uneven. That is, as the result of the elastic deformation of the respective trunnions 6, 6, the distances between the inner surfaces of the support plate portions 7, 7 of the respective trunnions 6 and the outer surfaces of the respective power rollers 11 become uneven. And, the thrust loads, which are applied to the rolling bodies existing in the portions where the distances between the trunnions inner surfaces and power roller outer surfaces are increased, are reduced; whereas, the thrust loads, which are applied to the rolling bodies existing in the portions where the distances are decreased, are increased. As a result of this, excessively large thrust loads are applied to some of the rolling bodies and thus the contact pressures between these rolling bodies and raceway surfaces with which the rolling surfaces of these rolling bodies are contacted become excessively large, which shortens greatly the fatigue lives of these rolling surfaces and raceway surfaces.
Also, stresses are easy to concentrate on the connecting portions A (see FIG. 8) between the pivot shafts 5, 5 serving as the rolling surfaces of inclined rolling bearings disposed on the two end portions of their associated trunnion 6 and the trunnion 6 for supporting the power roller 11; and, therefore, in case where an excessive large torque is input and thus, as described above, the trunnion 6 is elastically deformed, damage such as a crack can occur easily in the connecting portions A. In view of this, conventionally, there has been employed a structure in which the thickness of the trunnion 6 is increased to thereby prevent occurrence of such damage. However, this structure is not preferred, not only because the structure increases in size and weight but also because the cost thereof increases. Also, it is necessary to connect together the pivot shafts 5 and trunnion 7 with a radius greater than necessary, which raises a working problem.
Also, in case where the trunnion 6 is elastically deformed in such a manner as shown in FIG. 5, the displacement shaft 9 is inclined with respect to the trunnion 6. In this case, stresses concentrate on the engaged portion B (see FIG. 8) between the base end portion 9a of the displacement shaft 9 and trunnion 6, so that damage such as a crack is easy to occur in this portion. Also, in case where the displacement shaft 9 is inclined with respect to the trunnion 6, the position of the power roller 11 supported on the leading end portion 9b of the displacement shaft 9 is shifted so that the contact points between the peripheral surfaces 11a of the power rollers 11 and the inner surfaces 2a, 4a of the respective disks 2, 4 are shifted from their given positions, which in turn causes the transmission operation of the toroidal-type continuously variable transmission to be unstable.
To avoid the above drawbacks, in JP-A-2001-304366, there is proposed a technology in which, as shown in FIG. 9, on the inner surface side of the support plate portion 7 of a trunnion 6 on which a power roller 11 is situated, there is disposed a connecting member 33 which is used to connect together the leading end portions of a pair of bent wall portions 8, 8; and, the connecting member 33 is also used to restrict the trunnion 6 from being elastically deformed in the direction where the inner surface side of the support plate portion 7 of the trunnion 6 provides a concave surface.
In the thus-structured toroidal-type continuously variable transmission, a power roller unit 34 for the toroidal-type continuously variable transmission can be structured in the following manner; that is, after a displacement shaft 9, the power roller 11, a thrust ball bearing 24 and a thrust needle roller bearing 25 are assembled to the trunnion 6, the connecting member 33 is connected and fixed to the bent wall portions 8, 8 of the trunnion 6 by a fastening member such as a pin.
However, in the case of the above-mentioned conventional power roller unit 34, when assembling the power roller unit 34 into the toroidal-type continuously variable transmission, in case where the power roller 11 and outer ring 28 are moved toward the connecting member 33, there is a fear that the thrust needle roller bearing 25 can slip off from between the outer ring 28 and trunnion 6. This raises a problem that the toroidal-type continuously variable transmission incorporating such power roller unit 34 therein is poor in assembling efficiency.
Also, in case where the power roller unit 34 is assembled to the toroidal-type continuously variable transmission with the thrust needle roller bearing 25 remaining slipped off, the contact points between the power rollers 11 and the inner surfaces 2a, 4a of the respective disks 2, 4 are shifted and the transmission operation of the toroidal-type continuously variable transmission is thereby made unstable, which lowers the efficiency of the power transmission; and, in the worst case, the power transmission is impossible.